finding center

[brats.n.harleys]

OK, i have 4 pieces of 3/4'' round bar, 3'' long that need to be drilled, tapped, and counter sunk for 3/8'' bolts. they will be welded on to my motorcycle frame to mount the fender. bolts will go in from inside the fender. ive failed 3 times now finding center to drill it. i used x's on the pieces, center punched it, and put it in the drill press. it looks dead center when its just the small punch mark, but by the time it gets out to 3/8'' hole, its off a bit. It will still work, just irritates the hell out of me. What technique do you guys use? or a tool i don't know about? Thanks guys.

 

[rsanter]

I have a lathe that will do it

bob

 

[larry_g]

It sounds as if your finding center to mark it, but are you center drilling before you start your twist drill? You need a spotting or center drill

http://www1.mscdirect.com/CGI/NNPDF...T4NO=0&PMITEM=00412320&PMCTLG=00&PMT4TP=*LTIP

to start the hole to prevent the drill bit from 'walking'. If you don't have the proper tool do you have any stubbie drills? Anything short and stiff will help. Step drilling, starting with a small bit, and moving up in diameter will help also.

lg
no neat sig line

 

[brats.n.harleys]

I have a lathe that will do it

bob

lol i wish

 

[brats.n.harleys]

It sounds as if your finding center to mark it, but are you center drilling before you start your twist drill? You need a spotting or center drill

http://www1.mscdirect.com/CGI/NNPDF...T4NO=0&PMITEM=00412320&PMCTLG=00&PMT4TP=*LTIP

to start the hole to prevent the drill bit from 'walking'. If you don't have the proper tool do you have any stubbie drills? Anything short and stiff will help. Step drilling, starting with a small bit, and moving up in diameter will help also.

lg
no neat sig line

i was starting with a 1/16'' bit it is older though maybe ill stop by sears and get some new ones tomorrow, give that a try

 

[Sparkfarmer]

Sharp drill bits may fix the problem. The tool for the job (if you don't have a lathe) is a center head, heres the starrett combination square set that comes with one.

http://www.starrett.com/pages/1316_combination_square.cfm

Your local tool store should be able to sell one for a reasonable price, 5-30$ for a cheap one.

Good Luck

 

[larry_g]

Another problem that could arise is that the face of the shaft is not flat and perpendicular to the centerline of the spindle.

lg
no neat sig line

 

[A_Pmech]

Are you trying to drill though the side of the rod, or into the end?

Regarding locating holes on a flat plane by layout, begin by scribing your layout lines. Find the intersection of the layout lines by feel with a sharp scribe and twist it in.

Enlarge the point with a light center punch *****.

Drill a lead hole with a 1/32 to 1/16" drill, which will flex to follow the punch ***** rather than drill the side of the *****.

Drill the web clearance hole, if required.

Drill the final hole.

Any old machining textbook will also provide a good reference on laying out and drilling from the layout.

 

[Regnar]

Go to your local machine shop around lunch time. Bring a 6 pack and ask one of the guys to drill your holes on the lathe.

Almost everyone has given good advise. I would just offer up that you allow the drill bit to do all the work. If you force the drill bit in it will wander. I also recommend Machine Screw Drill bits. These drill bits are shorter and have less tendency to flex while feeding into material. Some will even say you dont have to step drill with them, but that is personal preference.

http://www.use-enco.com/CGI/INSRIT?PMAKA=240-6927&PMPXNO=4872142&PARTPG=INLMK32

Good Luck.

 

[metal1313]

i love machine screw drills because they are shorter and less likely to snap. i have some usa ones from enco actually and they are great for my limited use

 

[brats.n.harleys]

Thanks guys, Looks like I'll have some hunting to do after work tomorrow.

 

[gloveman132]

You really need a lathe or a mill with a digital read out.

It can also be done with an indicator mounted in the drill press. I use a coaxial center finder, you can get a cheap one from Enco for about $100.00, on sale now for $70.00.

http://www.use-enco.com/CGI/INSRIT?PARTPG=INLMKD&PMPXNO=952232&PMAKA=607-4907

A machine shop can do this in a matter of minutes and will probably charge you $20.00.

 

[djjsr]

I start precision holes with a countersink. It's pointed and will not walk. No centerpunch.

 

[mike13u]

You definately dont need a lathe and you dont need a mill. Those things just make it easier. Take your time and follow A Pmech's advice above. Scribe the lines with your center finder square. Punch the intersect of the lines. Now, if you want to make your life easier, get a centerdrill like this: to start the hole. Not necessary though. Take your time. You can do it without anything fancy.

 

[rylon]

I've also heard about putting your stock into the chuck of your drill press then lowering it into the vise and tightening the jaws of the vice. Then tighten the vise to the table of the drill press. Release your stock from the chuck and then put in the necessary pilot bit or center drill and you should be very close. Of course doing proper layout and everything else doesn't hurt.

Rylon